SOAPFaultException "MustUnderstand headers (oasis-200401-wss-wssecurity-secext-1.0.xsd) are not understood"

You could get this error when the service does not handle the headers. The service needs to implement a SOAPHandler with a getHeaders() that would resolve the headers. For the above mentioned fault the correct implementation would be as follows

 @Override 
    public Set<QName> getHeaders() { 
        QName securityHeader = new QName("http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd", 
                "Security"); 
        HashSet<QName> headers = new HashSet<QName>(); 
        headers.add(securityHeader);         
        return headers; 
    }

It is also possible to get this when the service is actually not secure, but the client is attempting to use security configuration (possibly using a XWSS security configuration) For this, just check the published wsdl from a browser and make sure it contains the expected security policy (append ?wsdl to its endpoint URL)

I found the solution. Following dependencies were required:

<dependency>
    <groupId>org.apache.cxf</groupId>
    <artifactId>cxf-rt-frontend-jaxws</artifactId>
    <version>2.2.3</version>
</dependency>
<dependency>
    <groupId>org.apache.cxf</groupId>
    <artifactId>cxf-rt-transports-http</artifactId>
    <version>2.2.3</version>
</dependency>

Good article on this topic and some pitfalls of cxf: http://www.logicsector.com/java/how-to-create-a-wsdl-first-soap-client-in-java-with-cxf-and-maven/